Bright orange screen grid
Posts: 404
Threads: 53
Joined: Feb 2009
kruc Wrote:Codefox, I'm keeping the same capacitance the sets were designed for, I just wondered if my 400v caps that were at their upper voltage limit. I don't have an issue with the slightly higher price of the 630volt caps, I just happened to get some 400v units at the time. I'm trying to stay away from electrolytics whenever possible when I rebuild a unit, that's why I'm using plastic caps whenever possible. FWIW, I found 600v plastic caps at AES. B+ shouldn't be an issue after replacing the filter with the same capacitance.
Music, my 20 lists a primary of 105-125volts. However at 125 the secondaries will put out a higher voltage than the tube filaments and plates were designed for. Recent threads on ARF discussed using a bucking transformer or a resistor in series with the primary. The obvious issues are finding space for a transformer or adequate area for heatsinking a wirewound resistor. I have a Japanese superhet with a 100v primary I run off a variac as I haven't gotten around to reducing the input voltage permanently.
Dave I don't know, but the Variac just struck me as a sure bet for protection, and though I know very little about how to use test gear, it does look impressive and makes me at least "feel" like a certified electronic tech! 8)
tractorforum.com *** I reserve the right to be wrong
Posts: 54
Threads: 1
Joined: May 2006
Wait until the first time you accidentally bump the variac knob and send 150 volts into your precious 70. You'll be looking for a better way to reduce voltage after the magic smoke clears.
Posts: 181
Threads: 0
Joined: Mar 2008
City: Pocasset, MA
Quote:In the 1939 season they began putting the output transformer under the chassis in most models. These tend not to survive while the speaker-mounted outputs are usually still good.
Could also be an outside supplier, where the earlier transformers were wound in-house.
115 volts was very common in the 1920s, but 120 and even 125 volts were standard in some areas. I have the exact percentages at home (I'm at work now).
Posts: 4,682
Threads: 51
Joined: Sep 2008
City: Sandwick, BC, CA
kruc Wrote:Codefox, I'm keeping the same capacitance the sets were designed for, I just wondered if my 400v caps that were at their upper voltage limit. I don't have an issue with the slightly higher price of the 630volt caps, I just happened to get some 400v units at the time. I'm trying to stay away from electrolytics whenever possible when I rebuild a unit, that's why I'm using plastic caps whenever possible. FWIW, I found 600v plastic caps at AES. B+ shouldn't be an issue after replacing the filter with the same capacitance.
Music, my 20 lists a primary of 105-125volts. However at 125 the secondaries will put out a higher voltage than the tube filaments and plates were designed for. Recent threads on ARF discussed using a bucking transformer or a resistor in series with the primary. The obvious issues are finding space for a transformer or adequate area for heatsinking a wirewound resistor. I have a Japanese superhet with a 100v primary I run off a variac as I haven't gotten around to reducing the input voltage permanently.
Dave
In my experience 400 volt condensers are usually fine in most old radios, I have a number of .047 mf 400 volt ones that I have used and none have failed. The typical plate voltage in an AC set isn't any more then 275 volts running, and maybe 350 volts on start up, most circuits will not see anywhere near that. One area where I would use a 630 volt unit is a situation where if the condenser fails that the B+ would short out of find a low resistance path to ground, some tone control circuits could have this happen. Electrolytics will work fine in place of a large paper condenser, just make sure that you get one of the right voltage and observe the polarity correctly.
For the Japanese radio I would take a look at junked printers, scanners, and other assorted consumer electronics for a bucking transformer, some were 25 or more volts at a high amperage, I would then build it into a box with a standard electrical outlet with the transformer in series with one side of the line.
Best Regards
Arran
Posts: 54
Threads: 1
Joined: May 2006
Arran, I'm using plastic caps to get away from electrolytics that dry out eventually. Same for paper caps as I've had them disintegrate before I could get both leads unsoldered. So much for testing a component that's in 2 pieces. I use better capacitors and higher tolerance resistors than Philco used so hopefully my radios will be playing long after I'm gone. My concern was only for the working voltage on my Philco 20's filter caps, but I've just gotten some Solen 630v units to replace the black mess I melted out of the can. For the Japanese radio, a wire wound resistor screwed to the chassis will be the simplest solution to get 100v to the primary.
Dave
Posts: 4,682
Threads: 51
Joined: Sep 2008
City: Sandwick, BC, CA
kruc Wrote:For the Japanese radio, a wire wound resistor screwed to the chassis will be the simplest solution to get 100v to the primary.
Dave
Dave;
A resistor may be a simple solution but I wouldn't call it the best, heat is the enemy of electronics and if you can avoid adding more of it it's a good idea. Suitable bucking transformers are just about everywhere for the taking, and all of the other parts needed are available from the local hardware store. I'm the sort who prefers to find a way to operate a radio as it was originally designed, even if using modern parts.
Best Regards
Arran
Posts: 54
Threads: 1
Joined: May 2006
The Japanese radio was a kit I bought in Akihabara in 1991. The directions are in Kanji, and it was a fun mental exercise to put together. Akihabara is a neighborhood in Tokyo with small shops that sell caps, resistors, transformers, tools, tubes, kits, and computers. I wish I had a place like it that I could visit for parts, though the closest example in this country was probably the old Radio Row in NYC. As the radio is only a black steel chassis with an aluminum faceplate, a gold ww resistor wouldn't hurt it even if it here mounted on the back.
Dave
Users browsing this thread: 1 Guest(s)
|
Recent Posts
|
Jackson 715 not working
|
Mrfixr55, its working now. I cleaned the switches and sockets with spray cleaner. Thanks for helping on this one.daveone23 — 06:26 PM |
Jackson 715 not working
|
Now that you posted the schematic, I don't know why that Sprague electrolytic cap is across the meter, as it is not indi...MrFixr55 — 05:51 PM |
HiFi (Chifi) tube amp build - but my own design.
|
What may be lacking in the PP Tube amps may be the 2nd harmonics, which some, especially RCA back in the day called &quo...MrFixr55 — 05:32 PM |
Jackson 715 not working
|
Usually in an emission tester, the tube under test is measured as if it were a diode. So, some testers connect all the g...RodB — 04:17 PM |
Restoring Philco 37-604C
|
Yep. F5 is green, D5 is Red.
Red is Bad.
Green is Clean.morzh — 01:30 PM |
Jackson 715 not working
|
I did start to do that but I stalled out because I could not figure out how the grid and plate get voltage. In this diag...daveone23 — 11:52 AM |
Restoring Philco 37-604C
|
(Insert Homer Simpson "DOPF" Here.)
When all fails, look at the can. Took the Ron Ramirez advice, red Caig D...MrFixr55 — 09:23 AM |
Philco 91 Speaker Replacement
|
From your text I am not sure if you intend to use the existing speaker with a resistor instead of the field coil.
It wo...morzh — 08:44 AM |
Philco 91 Speaker Replacement
|
My field coil is bad. I am still hoping to find an original, but if I can't I will go with a fitting Philco speaker, 125...dconant — 08:34 AM |
Philco 91 Speaker Replacement
|
As Rod said, it is OK to use a fitting speaker, and then look for an original one.
If you buy a Hammond 125 output tr...morzh — 08:15 AM |
Who's Online
|
There are currently 3803 online users. [Complete List] » 3 Member(s) | 3800 Guest(s)
|
|
|
|